Wave transmission system



April 3, 1934. J G, ACEVES 1,953,455

WAVE TRANSMISSION SYSTEM Filed April 6, 1932 INVENTOR BY A? v 4A'I'I'ORN EYS Patented Apr. 3. 1934 WAVE TRANSMISSION SYSTEM JuliusGourgues Aceves, New York, N. Y., as-

signor to Revelation Patents Holding Company, NewYork, N. Y., acorporation of Delaware Application April 6, 1932, Serial No. 603,467 11Claims. (01.179-171) This invention relates to electrical transmissionsystems and with particularity to wave repeating systems employingelectron discharge devices.

The invention is in the nature of an improvement on the type of systemdisclosed in applica-- tion Serial No. 394,172, filed September 21,1929, and application Serial No. 533,396, filed April 28, 1931.

There are disclosed in said applications systems employing a pluralityof sets of triode elements so connected that the grid of the second setmay utilize a positive grid swing without producing noticeabledistortion in the output. The generic circuit arrangements are such thatthe grid of the second triode set is inherently positive with respect toits cathode. Under normal conditions of tube design there is, therefore,a considerable flow of steady space current between the cathode andanode of the second triode set.

In order to take full advantage of the improved operating features ofthe generic system, and at the same time out down the normal platecurrent of the second triode set, it is suggested in application SerialNo. 533,396, to maintain the second grid at or near ground potential bymeans of a choke coil connected between the said grid and ground. Whilethis latter suggestion achieves a maximum power amplification from thesystem, with a. minimum of distortion, it nevertheless complicates thecircuit connections. Furthermore, as the full advantages of the systemrequire a choke coil which is of minimum ohmic resistance and of high A.C. impedance to the signal frequencies, the cost of such a choke isconsiderable as compared'with the remaining elements of the system.

Accordingly it is one of the principal objects of this invention toprovide a novel method of maintaining the grid of a tube at apredetermined working point on the grid current-plate voltagecharacteristic.

Another object of the invention is to provide a method of utilizing theoutput voltages of a triode to maintain the static grid potential.

Another object of the invention is to provide a novel method ofutilizing an inductance coupled to the output of a triode formaintaining the grid at a substantially fixed base potential.

A feature of the invention relates to a system employing a pair oftriodes in cascade, wherein signal coupling between the triodes isefiected through the intermediary of a coil coupled to the outputcircuit of the second triode.

Another feature of the invention relates to a system employing a pair oftriodes in cascade an anode 6. The grid 5 is directly connected towherein the grid losses of the second triode are supplied by thecathode-anode of the first triode, and wherein the signal variations areimpressed upon the second grid under control of the output of the secondtriode.

Another feature relates to a wave signaling system employing a pair oftubes in cascade, wherein the first tube supplies the grid losses of thesecond tube, and wherein the output transformer of the second tube alsoacts as an input coupling element for said second tube.

A further feature of the invention relates to a system employing a pairof tubes in cascade, in conjunction with an outputtransformer having asecondary winding connected between the grid and cathode of the saidsecond tube.

A still further feature relates to the novel organization andarrangement of elements which go to make up a cheap and emcient poweramplifier and/or detector system employing a minimum number of tubes andrelatively simple circuit connections.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detail descriptions andthe appended claims.

Referring to the drawing,

Fig. 1 is a schematic diagram of the generic type of system to which theinvention is suited;

Fig. 2 is a diagrammatic circuit drawing to explain the operation of thecoupling idea of the invention; and

Fig. 3 represents schematically a complete amplifier and/or detectorstage embodying principles of the invention. I

Referring more particularly to Fig. 1, there is shown the generic typeof system to which the invention is adapted. For a detail description ofthis system reference may be had to the application Serial No. 533,396.Suifice it for the present to state that the system is intended toutilize two sets of triode elements the first set-comprising an electronemitting cathode 1, a control electrode2, and an anode 3; the second setlikewise comprising an electron emitting cathode 4, a grid 5 and thecathode 1, as by means of a wire 7. The signals to be repeated areimpressed across the grid 2 and the cathode 1, as indicatedschematically by the numeral 8. Connected between the cathode 1 and thenegative terminal 9 of the anode potential source (or ground) is a chokecoil 10 which is of minimum ohmic-resistance, but has a maximum A. C.impedance at the signal frequencies. It will be noted that the choke 10is connected in parallel with the space between the cathode 4 and grid5, consequently the grid 5 is maintained at or near ground potential andthe signal variations that are impressed upon the grid 5 merely vary theconductivity of the space between the elements 4 and 6. Inordinarycoupling circuits, current flow between the elements 4 and 5 would causea distortion in the output of the device. However, in the circuitarrangement shown in Fig. 1, this current flow or loss between elements4 and 5 is compensated for by the current flow between the elements 3and 1 of the first triode set. In other words, by means of theinductance 10 it is possible to maintain the grid 5 at or near staticground potential, and at the same time the grid 5 may swing positivelyunder control of the signal wave, without producing distortion. One ofthe important features of this circuit is the fact that the load of thefirst triode set is between the cathode 1 and the negative terminal 9 ofthe anode supply (or ground) this load being directly across the gridcathode of the second triode set. Consequently the variations insignaling potential impressed on grid 2 cause corresponding variationsbetween the elements 3 and 1, resulting in similar alternating potentialvariations being set up across the inductance 10. It is also significantto note that the potential variations on both the grid 2 and the grid 5are always in phase, whereas in the ordinary coupling circuits thesegrid potentials are 180 out of phase.

However, the above described circuit requires in addition to the usualoutput transformer the relatively expensive choke coil 10, and requiresadditional connections apart from the output transformer. It has beenfound that the beneficial efiects as regards undistorted power output ofthe system of Fig. 1 may be achieved without employing an expensivechoke coil 10. For the purpose of explaining this feature reference maybe had to Fig. 2. However, prior to considering Fig.2, it should benoted that the choke coil 10 of 1 have an ohmic drop that is very small.

Fig. 1 should preferably be such that the impedance between cathode 1and ground should theothe choke 10 must have a low resistance at zerocycles and high impedance at any audio frequency within the usual rangerequired for faithful tone reproduction. If, therefore, some means canbe found for introducing a counter E. M. F. between the grid 5 and thecathode 4, which will have the same eii'ect as the impedance drops inthe choke 10, at the same time providing a low I. R. drop for the steadycurrent, a much cheaper and more emcient system can be designed, both asregards power output and faithfulness.

Fig. 2 illustrates schematically one method of achieving this result. Inthis figure the elements 4, 5 and 6 correspond to the second set oftriode elements of Fig. 1. If there is impressed across the elements 4and 5 of Fig. 2 an electro-motive force of sinusoidal character (eithersimple harmonic or complex) another corresponding electro-motive forcewill be set up between the electrode 4 and the electrode 6 through theprimary winding 11 of the output transformer. If we assume thetransformer 11 to be a perfect or ideal transformer working into aresistance load R, the electro-motive force across the primary winding11 will be approximately 180 out of phase with respect to the impressedE. M. F. If the output transformer is provided with another or auxiliarywinding 12 there will be induced across it an E. M. F. corresponding tothe impressed E. M. F., and the phase relation of which will bedetermined by the polarity of the connections from the winding 12.Preferably this winding 12 has one terminal connected to the cathode 4(or ground). Consequently the diiference of potential across the points13, 14 will be the resultant of the impressed signal potential and theinduced potential in the winding 12. The voltage across the primarywinding 11 is in accordance with the standard formula In the aboveequation, E equals the voltage developed across the primary winding 11by the impressed E. M. F. from the source 15 represented by e; 1!.equals the amplification factor of the tube; R is the load resistance;Tp equals the internal impedance of the triode, N11 equals the number ofturns in the primary 11, N16 equals the number of turns in the secondary16. The voltage induced across the winding 12 is given by the followingequation;

where the induced voltage is represented by er, and where N12 equals thenumber of turns in the auxiliary winding 12.

Then by substituting, we find- N11 2 N11 an This shows that when theother factors remain as fixed values, the voltage developed across theauxiliary winding 15 varies proportionately to the impressed E. M. F.

From the foregoing equations, it is possible to calculate the ratio oftransformation of the windings of the output transformer. Preferably thesystem is arranged such that the voltage given by 12 the Equation (3) isequal and opposite to the impressed E. M. F., in consequence of whichthe difference of potential between points 13 and 14 will always bezero.

Consequently considering the output transformer as an ideal transformerthe circuit will function the same whether the points 13 and 14 aredisconnected from each other or are short circuited to each other. Underthis condition of adjustment therefore we have the functional effect ofthe choke 10 without the necessity of having a choke of very low ohmicresistance and high A. C. impedance. The winding 12 produces an E. M. F.corresponding to the counter E. M. F. in the choke 10 of Fig. 1, and themagnitude of this E. M. F. may be designed economically merely by theratio of transformation between the windings 11 and 12. Preferably, theohmic resistance of the winding 12 should be of the same value as thatof the choke 10 of Fig. 1.

The above explanation is of course predicated on the assumption that theoutput transformer is an ideal transformer. However, by means ofsuitable resistances this ideal condition may be very closely simulatedin actual practice.

Accordingly in Fig. 3 there is shown a complete amplifier systememploying the idea disclosed in Fig. 2. In Fig. 3 the signals to beamplified are impressed by means of the input transformer 17 upon thegrid 18 of the first triode set. The grid 18 is connected through thecondenser 19 to the cathode 20 and the static bias of the said grid 18may be provided by means of the drop through the resistance 21. Thecondenser 19 is preferably of suflicient capacity to afford a very lowimpedance to the impressed signal variations. for example a 2 mfg.condenser maybe employed. The direct current path from the grid 18 tothe cathode 20 includes the resistance 22, which is preferably highenough to prevent the cathode being substantially short circuitedthrough condenser 19 to ground. Any suitable so1u-ce of operatingpotential may be connected across the terminals 23 and 24. While Fig. 3shows a single source of potential for the anodes and filaments, it willbe understood that this is not absolutely necessary, and that thefilaments 25 and 26 may be connected in parallel to a separate source ofheating current. However, it has been found that the arrangement shownin Fig. 3 enables a very simple and cheap unit to be constructed. Inthis figure the heater filament 25 for the cathode 20, is connected inseries with the filament emitter 26 of the second triode set, and alsoin series with a resistance 27 for supplying the proper voltage to thefilaments in series.

The positive terminal 23 of the supply source is connected to the anode28 of the first triode set, and also to the anode 29 of the secondtriode set, through the primary winding 30 of the output transformer. Asdescribed in application Serial No. 533,396, the cathode 20 is connecteddirectly by wire 31 to the grid 32 of the second triode 'set. For thepurpose of maintaining a preselected normal static grid bias on theelectrode 32 there is provided a resistance 33 which is connected inseries with the auxiliary secondary winding 34 to the negative terminal24 of the source of supply (or ground). This resistance 33 not only.serves to give the proper bias to grid 32, but also functions tocontrolthe degree of coupling between grid and plate circuits to compensate forthe deviance of the said transformer from the 'ideal characteristic.Connected across the auxiliary winding 34 is a resistance 35, preferablyadjustable, for equalizing the operation of the transformer at varioussignal frequencies. The resistance also acts to compensate for the factthat the load B. may not be a pure resistance load. In one actual set upthat was found to produce proper results the resistance 35 had a valueof from 2000 to 5000 ohms and the ratio of transformation between thewindings 30 and 34 was 1.5 to 2. It was found that when the winding 34was replaced by a choke coil connected similarly to coil 10 (Fig. 1)music was reproduced, but the gain was 5 decibels less than thatobtainable with the circuit arrangements of Fig. 3. The resistance 35also functioned to suppress audio frequency oscillations.

The manner of working of the system of Fig. 3 is in generalsubstantially the same as that described in application Serial No.533,396. Signals impressed on the grid 18 result in correspondingvariations of current between the electrodes 28 and 20. Consequently thepotential of the cathode 20 varies in correspondence with the signalsimpressed on the grid 18. Inasmuch as the cathode 20 is directlyconnected to the grid 32, this latter grid also will undergo potentialvariations corresponding to the signals impressed on grid. 18, andfutrhermore, the potential variations on the grids 18 and32 will be insubstantial phase. The result is that there is impressed across the grid32 and the cathode 26, signal potentials which produce correspondingchanges in the current flow between the said electrodes 26 and 32. Theretends to flow between the elements 26 and 32 a steady current similar tothe current between the elements 20 and 28, even when no signal wavesare being impressed. However, when the winding 34 is connected incircuit as shown. there is induced an E. M. F. corresponding to thesignal waves which is 180 out of phase with the waves impressed on thegrid 32, so that during the passage of signal variations the grid 32 ismaintained at substantially its selected static bias potential. Since,however, the winding 34 is connected across the elements 26 and 32 itproduces a counter E. M. F. corresponding to the signal variations, andthus controls the current in the output windings 30 and 36.Functionally, therefore, by the proper connection of the winding 34there is achieved the effect of the low resistance choke 10 of Fig. 1,without materially affecting the overall gain of the system.

As a matter of fact, with the proper selection of resistance 33 andwindings 30 and 34, greater power agnplification is attained with thecircuit of Fig. than is attainable with the circuit of Fig. 1, atv thesame time reducing the cost of the apparatus. The winding 34 providesthe direct current I turn path between grid 32 and cathode 26, similaglyto-the choke coil 10 of Fig. 1. However, inst ad of relying on theself-inductance or auto-transformer action of the choke to affect thesignal coupling between the tubes, reliance is placed upon the inductivetransformer action between windings 30 and 34 to provide the samecounter E. M. F. as would be provided by the choke. This is accomplishedby choosing the right polarity of connections from the winding 34 to thegrid 32 and cathode 26.

It will be understood, of course, that the invention is not limited toan arrangement wherein the winding 34 feeds back voltages equal to thesignal waves.

Various modifications may be made without departing from the spirit andscope of the invenion.

Furthermore, while it is preferred to mount the two sets of triodeelements of Fig. 3 in the same evacuated container, this is notnecessary as the triode elements may be mounted in separate containersand interconnected as disclosed in Fi 1.

Furthermore, while an indirectly heated cathode 20 is shown for thefirst tube, it will be understood that the invention is. not limitedthereto, but that any other well known form of electron emitting cathodemay be employed in the first triode set and in the second triode set.

Furthermore, the invention is not limited to a tube having only threeelements since it may be applied to tubes having other electrodes inaddition to the usual triode electrodes, for example so calledshield-grid tubes, pentode tubes, space discharge tubes, etc.

What is claimed is:

1. A wave repeater comprising a first set of triode elements, a secondset of triode elements, the load of the first set being directly acrossthe grid and cathode of the second set, said load including an impedancecoupled to the output circuit of the second set.

2. A wave repeater comprising a first set of triode elements, a secondset of triode elements, the load of the first triode set existingbetween the cathode and the negative terminal of the anode supply, saidload including an inductance coupled to the output circuit of the secondtriode set.

3. A wave repeater comprising a first triode set, a second triode set,the input impedance of the second triode set being directly across theload of the first triode set, said load including an impedanceinductively coupled to the output circuit of the second set.

4. A wave repeater comprising a first triode set, a second triode set, adirect connection between the cathode of the first set and the grid ofthe second set, an output transformer for the second set, saidtransformer having a winding connected between the grid and cathode ofthe second set.

5. A wave repeater comprising a pair of triode sets, circuitarrangements including a short circuit connection from the cathode ofthe first triode set to the grid of the second triode set and a sourceof anode potential for causing the grid of the first set to bepermanently negative with respect to its cathode, while allowing thegrid of the second set to swing positively with respect to its cathode,an input coupling element connected across the grid and cathode of thesecond set, and means for inducing into said element voltages undercontrol of the output of the said second set.

6. A wave repeater comprising a first triode set, a second triode set,an output transformer for said second set, said transformer having aprimary winding, a secondary output winding, and an auxiliary secondarywinding on said transformer serving as a direct current return betweenthe grid and cathode of the second set, and also as an input impedancefor the said second set.

7. A wave repeater comprising a pair of triode 1,953,455 sets, an outputtransformer forthe second set,

a winding on said transformer having one terminal conductlvely connectedto the cathode of the first set and the grid of the second set, theother end of said winding being conductively connected to the cathode ofthe second set.

8. A wave repeater comprising a first triode set, a second triode set,an output transformer for said second set, and means including a wind-'ing on said transformer for maintaining the grid of the second set atsubstantially static ground potential.

9. A wave repeater comprising cathode, grid and plate elements, secondcathode, grid and plate elements, the load of the first elements beingdirectly across the second grid and cathode, said load including animpedance coupled to the output circuit of the second elements.

10. A wave repeater of the electron discharge type comprising cathode,grid and plate elements, second cathode, grid and plate elements, anoutput transformer for said second set of elements, an auxiliary windingon said transformer providing part of the direct current return path forboth the grid to cathode of the said second set of elements and thecathode of the sa d first set to the negative terminal of the anodesupply.

11. A wave repeater of the electron discharge type comprising cathode,grid and plate elements, second cathode, grid and plate elements, theoutput load for the first set of elements existing between its cathodeand the negative terminal of the anode supply, said load including animpedance coupled to the output circuit of the said second set ofelements, and said impedance being also common to the grid-cathode inputof the said second set of elements.

JULIUS GOURGUES ACEVES.

